The present invention relates to a low pressure carburization process applied to metal alloy parts and more particularly steel parts, as well as to an installation permitting the performance of said process.
Carburization is widely used in metallurgy, when it is a matter of hardening the surface of metal parts over a certain depth, while excluding the internal portions thereof, which must retain a certain flexibility so as not to inopportunely break. According to a standard metallurgical process carbon is incorporated by gaseous carburization.
As is more particularly described in the Hayes French Patent 2 154 398, the articles to be carburized are placed in a vacuum furnace, in which circulation takes place of gaseous hydrocarbons essentially based on methane or propane and treatment only takes place at temperatures above approximately 950.degree. C. Working takes place at a pressure below atmospheric pressure. This ensures the absorption and thermal diffusion of the carbon on the surface of the article. It should be noted that the performance of this process involves the need to use a pulsation effect for diffusing the carbon to the desired depth in the treated part.
According to a process described in the Ipsen Patent 2 361 476, use is also made of a methane-based fuel gas. The latter suffers from the disadvantage of dissociating, while producing a large amount of carbon, which is transformed into lampblack and hinders carburization by dirtying the treated parts and also the furnace.
Other furnace designers still use a vacuum plasma discharge to attempt to obviate the difficulties inherent in the use of the aforementioned hydrocarbons and this is known as ionic carburization.